Amorphous material for active elements exhibiting a memory effect

ABSTRACT

An amorphous material or composition actively exhibiting a memory effect, comprising As 28.9-55.0 atomic %, Se 30.0-63.0 atomic %, Cu 3.0-12.0 atomic % and Au 2.8-6.0 atomic %.

Asahara et al.

Hoya Glass Works, Ltd., Tokyo, Japan Filed: July 10, 1972 Appl. No.: 270,405

Assignee:

Foreign Application Priority Data July 8, 1971 Japan .46/50504 U.S. Cl 75/134 H, 75/134 P Nov. 13, 1973 [58] Eield of Searcli .I' 75/134 H, 134 P; 7 96/1 .5

[5 6] References Cited UNITED STATES PATENTS 2,822,300 2/1958 Mayer et a] 117/201 3,524,745 8/1970 Cerlon et al. 3,615,413 10/1971 Fisher et al. ..96/1.5

Primary Examiner-L. Dewayne Rutledge Assistant ExaminerE. L. Weise Att0mey-Richard C. Sughrue et a1.

[57] ABSTRACT An amorphous material or composition actively exhibiting a memory effect, comprising As 28.9-55.0 atomic Se 30.0-63.0 atomic Cu 3.0-l2.0 atomic and Au 2.8-6.0 atomic 1 Claim, 2 Drawing Figures PAIENIEU nnv 1 3191s HGI 5'0 VOLTAGE AMORPHOUS MATERIAL FOR ACTIVE ELEMENTS EXHIBITING A MEMORY EFFECT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an amorphous material or composition for active elements having a memory effeet.

2. Description of the Prior Art One known amorphous material for active elements exhibiting a memory effect, in which the resistivity can be electrically switched from a high resistance state (10 Qcm) to a low resistance state (10 10 0 cm) and the latter state is maintained in the absence of any bias current after the switching current has been removed, produced by adding Ge or Si to an As-Te alloy, is readily crystallized and it keeps its amorphous property only with difficulty. Further, the melting of infusible Ge and Si to a uniform melt of Ge-Si alloy is extremely difficult.

On the other hand, an amorphous As-Te material is known to have a switching property, and is able to keep a stable amorphous structure. However, it has a high threshold voltage.

SUMMARY OF THE INVENTION The inventors have discovered that the addition of Cu to an amorphous As-Te material is effective to lower its threshold voltage, and a patent application relating to such As-Se-Cu material was filed as Japanese Patent Application 1 17,167/70. But there is only a switching action in this system, and a low resistance state can be realized under the application of bias current. The present invention is based upon the further discovery that the addition of Au to such an As-Se-Cu material makes the low resistance state stable in the absence of any bias current, resulting a favorable memory effect with a low threshold voltage.

The amorphous material of this invention for an active element exhibiting a memory effect is produced by melting a mixture composed of As 28.0-55.0 atomic Se 30.0-63.0 atomic Cu 13.0-12.0 atomic and Au 2.0-6.0 atomic If the amount of As and of Se are beyond the above restricted ranges, the molten matter is readily crystallized and it is difficult to keep a stable amorphous structure. Less than 3.0% of Cu is ineffective to lower the threshold voltage and it is impossible to obtain an Au dissolved amorphous material. More than 12% Cu causes crystallizing of the amorphous material and one cannot keep the amorphous structure .2.06.0% of Au is a necessary ingredient to impart the memorizing property to the resulting amorphous material. Less than 2.0 percent of Au is not effective to cause the memory effect and more than 6.0 percent of Au causes readily crystallizing melts.

BRIEF DESCRIPTION OF THE FIG. 1 shows an electric circuit for measuring the characteristics of an amorphous active element according to this invention.

FIG. 2 is a diagram of the voltage-current characteristics of the amorphous material of this invention.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1, A is a test specimen of the amorphous active element, E is an electric source for generating a bias voltage, 8,, S and S are switches, R, is a series load resistor, Rs is a standard resistor for measuring the electric current, C is a condenser, V shows the voltage applied to the amorphous active element, and I shows the electric current passing through the amorphous active element.

In FIG. 2, curve 1 shows the voltage-current characteristics of the specimen in the high resistance state, curve 2 shows the voltage-current characteristics of the specimen in negative resistance state, and curve 3 shows the voltage-current characteristics of the specimen in the memory state.

For example, one of the specimen A of the active element can be produced by depositing Au vapor on a surface of a thin film of the amorphous material in vacuum. The specimen A is set in the electric circuit and the bias voltage E is applied to the specimen A by closing the switch S and opening switches S and S As the bias voltage E is increased, both voltage V and electric current I increase along curve 1 in FIG. 2, which shows the peculiar resistance p off in the high resistance state. After reaching a certain level (threshold voltage Vth), the voltage V decreases along the load resistance curve 2 in FIG. 2, which is determined by the series load resistance R The electric current I still increases, and a negative resistance appears, i.e., the high resistance state is switched to the low resistance state. The low resistance state of specimen A is maintained even after the bias voltage E is extinguished, and the voltagecurrent characteristics, as shown in curve 3 in FIG. 2, emerges upon the next application of the bias voltage E to specimen A. The resistivity p at the memory state is shown by curve 3 is constant and extremely stable irrespective of the change of the load resistance R In order to extinguish the memory state of specimen A thus obtained, the switch S is opened and switch S is closed to apply the bias voltage E to the condenser C, and then the switch S is opened and the switch S is closed to instantaneously apply a voltage (V on the specimen A in the memory state and to flow an electric current exceeding greater than a particular critical value for the composition.

The resistivity poff and the threshold voltage Vth of specimen A in the high resistance state after the memory is extinguished in the manner described above are the same as their starting values. In addition, resistivity p of the specimen A in the memory state obtained by switching again becomes the same value as in the 1st memory state. Thus, the memorizing and erasing of the specimen A can be carried out sharply and quickly.

Some examples of the amorphous elements according to this invention are shown in Table 1, and the cycle test between p and p for Specimen No. 3 in Table 1 is shown as an example in Table 2.

TABLE 1.SPE(1MEN COMPOSITION (ATOM. PERCENT) Parr P .\1 Vth R r. (11 As Se Au 1Q-cml (fl-cm) 41 v/mrn) {Q1 1... 9.5 28.6 57.1 4.8 1.59 X l 2.48 X 10" 1090 6 10" 2.. 9.5 33.3 52.4 4.1% 4.36 l0 5.96 X 10" 2000 8 X 10" 3.. 9.5 42.8 42.8 4.8 1.58 1 10 9.37 X 10" 1290 10" 4.. 9.5 52.4 33.3 4.8 6.16 X10 2.15 X 10 1020 2 X 10" 5.. 4.8 28.6 61.9 4.8 1.18X10" 1.58X10 7130 10 6.. 5.0 36.0 54.0 5.0 9.98 X 10" 1.82 X 10- 8240 6 X 10 7 9.7 43.7 43.7 2.9 3.23 10 1.55 X 10 2890 10" TABLE 2 V,- R: Purl Vih R11 PM 1v] ifl (from) (v/rnml [Q1 ((L I memorized 6.16 X 10- 900 2 X 10 2.15 X 10 S {erased 250 2 X 10- memorized 6.15 X 10 900 2 X 10- 2.01 X 10-" 2nd erased 200 2 3 d memorized 6.15 X 10- 890 2 X 10-- 2.06 X 10 erased 250 2 10 k V,. is the pulse voltage. i i

The amorphous material for an active element of the a relatively low temperature with ease, and keeps its present invention is produced in such a manner that a amorphous structure. powdered raw material on each ternary compone is While this invention has been described with refer- Sealed a quartz tube having an Inner dlametel' of ence to particular embodiments thereof, it will be un- 6 mm and a length of 50 mm under a Vacuum, the raw derstood that the numerous modifications may be materials in the thus sealed tube are melted in an elecmade by those Skilled in the art without amuauy depart tric furnace at a temperature of from 850C to 950C m from the Scope of the invention. for 3 hours whlle stlrrlng the molten 1 P Therefore, the appended claim is intended to cover resuhmg "when mammals are quenched m 1 an all such equivalent variations as coming within the true then the thus produced amorphous materials are respirit and Scope of the invention moved from the quartz tube. The material obtained can what is claimed is I be formed to the desired shape while belng reheated in L An amorphous material for the production of a 2 gas Streamtive element having a memory effect including an elecr amorphous material of this mvent'on thus trically bistable state composed of 27.0-55.0 atomic tamed has a low threshold voltage and excellent mem- As, atomic Se, 3-0420 atomic Cu and cry effect and can be memorized and erased repeat- 2-0450 atomic ALL edly. Further, this amorphous material can be fused at 40 

